1. Field of the Invention
The present invention relates to a line thermal head letter printing method of a synchronous type for making a letter printing by feeding a hot release type thermal transfer ribbon tape following a transfer velocity of a print object sheet and especially relates to a line thermal head letter printing method in which feeding and winding of the ribbon tape are improved.
2. Description of the Prior Art
In recent years, there are often cases where letters and marks, such as date of manufacture, tastable time period and series number of manufacture, are printed on a packaging material differently for each of objects to be printed. In such cases, the printing is often done by feeding a hot release type thermal transfer ribbon tape following a transfer velocity of a sheet as an object to be printed, such as a packaging material film, (herein referred to as "a print object sheet") and by supplying a line thermal head, such as that called a corner edge type or an end face type, which is pressed against the ribbon tape, with electricity.
In case the printing is done on the print object sheet, which is being transferred with a high velocity, by the line thermal head using the hot release type thermal transfer ribbon tape, when a portion to be printed of the print object sheet comes, it is necessary that the ribbon tape is wound to be fed synchronously with the velocity of the print object sheet. For this purpose, that is, in order to wind the ribbon tape to feed it synchronously with the velocity of the print object sheet in time for start of the printing, a rise time is needed.
Because of such rise time, there is necessarily caused a delay in the start of the winding of the ribbon tape. Despite such delay in the start of the winding of the ribbon tape, as the ribbon tape, which is in contact with the print object sheet, is fed upon start of the printing, there may be caused a loosening of the ribbon tape hot release portion at a tip of the head in the initial stage of the printing immediately after the start of the printing, which often results in the problem that there is caused a place where no printing is done at a head portion of the printing or the printing is out of order because of no good hot release, and it has been found that this problem arises in the case where the printing is done on the print object sheet which is being transferred at a high velocity of 10 inch/second or more.
As mentioned above, in the conventional letter printing method for printing letters by using a line thermal head supplied with electricity and a hot release type thermal transfer ribbon tape, there is a problem that a printing of a desired quality may not necessarily be done at the starting time of the printing.